Optical emission spectroscopy (OES) for remote plasma monitoring

ABSTRACT

Methods and systems for etching substrates using a remote plasma are described. Remotely excited etchants are formed in a remote plasma and flowed through a showerhead into a substrate processing region to etch the substrate. Optical emission spectra are acquired from the substrate processing region just above the substrate. The optical emission spectra may be used to determine an endpoint of the etch, determine the etch rate or otherwise characterize the etch process. A weak plasma may be present in the substrate processing region. The weak plasma may have much lower intensity than the remote plasma. In cases where no bias plasma is used above the substrate in an etch process, a weak plasma may be ignited near a viewport disposed near the side of the substrate processing region to characterize the etchants.

FIELD

Embodiments disclosed herein relate to remote plasma etch processes.

BACKGROUND

Integrated circuits are made possible by processes which produce intricately patterned material layers on substrate surfaces. Producing patterned material on a substrate requires controlled methods for removal of exposed material. Chemical etching is used for a variety of purposes including transferring a photoresist pattern into underlying layers, thinning layers or thinning lateral dimensions of features already present on the surface. Often it is desirable to have an etch process which etches one material faster than another helping e.g. a pattern transfer process proceed. Such an etch process is said to be selective of the first material relative to the second material. As a result of the diversity of materials, circuits and processes, etch processes have been developed with a selectivity towards a variety of materials.

Dry etch processes are often desirable for selectively removing material from semiconductor substrates. The desirability stems from the ability to gently remove material from miniature structures with minimal physical disturbance. Dry etch processes also allow the etch rate to be abruptly stopped by removing the gas phase reagents. Some dry-etch processes involve the exposure of a substrate to remote plasma by-products formed from one or more precursors. Remote excitation of etchants in a remote plasma system (instead of locally) may desirably increase selectivity.

Methods and systems are needed to monitor aspects of remote plasmas in-situ for a variety of purposes.

SUMMARY

Methods and systems for etching substrates using a remote plasma are described. Remotely excited etchants are formed in a remote plasma and flowed through a showerhead into a substrate processing region to etch the substrate. Optical emission spectra are acquired from the substrate processing region just above the substrate. The optical emission spectra may be used to determine an endpoint of the etch, determine the etch rate or otherwise characterize the etch process in-situ. A weak plasma may be present in the substrate processing region. The weak plasma may have lower intensity than the remote plasma. In cases where no bias plasma above the substrate is used in an etch process, a weak plasma may be ignited near a viewport disposed near the side of the substrate processing region to characterize the etchants.

Embodiments disclosed herein include methods of etching a substrate. The methods include placing the substrate in a substrate processing region of a substrate processing chamber. The methods further include flowing a fluorine-containing precursor into a remote plasma region separated from the substrate processing region by a showerhead. The methods further include forming a remote plasma having a remote plasma power in the remote plasma region. The methods further include producing plasma effluents from the fluorine-containing precursor in the remote plasma in the remote plasma region. The methods further include flowing the plasma effluents through the showerhead into the substrate processing region. The methods further include etching the substrate with the plasma effluents. The methods further include forming a local plasma having a local plasma power in the substrate processing region. The methods further include acquiring an optical emission spectrum through a viewport affixed to a side of the substrate processing chamber, the side forming a border of the substrate processing region. The optical emission spectrum represents intensity as a function of optical wavelength and the optical emission spectrum is acquired with an optical emission spectrometer.

The remote plasma power of the remote plasma may exceed the local plasma power of the local plasma by a factor of ten or more. The local plasma may be centered over the substrate. The local plasma may be positioned above the substrate and outside an edge of the substrate near the viewport. The local plasma may be formed using an electrode located on the outside of the viewport and the local plasma power may be applied between the electrode and the substrate processing chamber. The local plasma may be formed using a first electrode and a second electrode, each positioned on the outside of the viewport and the local plasma power may be applied between the first electrode and the second electrode.

Embodiments disclosed herein include substrate processing chambers The substrate processing chambers include a remote plasma region. The remote plasma region is configured to receive a fluorine-containing precursor and form a remote plasma from the fluorine-containing precursor. The substrate processing chambers further include a remote plasma power supply configured to apply a remote plasma power to the remote plasma region and configured to form the remote plasma. The substrate processing chambers further include a substrate processing region. The substrate processing chambers further include a showerhead positioned between the remote plasma region and the substrate processing region. The substrate processing region is fluidly coupled to the remote plasma region by through-holes in the showerhead. The substrate processing chambers further include a pedestal configured to support a substrate. The substrate processing chambers further include a flange attached to the substrate processing chamber. The flange forms a vacuum seal with the substrate processing chamber. The substrate processing chamber further includes a viewport attached to the flange forming a vacuum seal with the flange. The viewport is optically transmissive in a near infrared spectrum. The substrate processing chambers further include an optical emission spectrometer configured to receive optical radiation after the optical radiation passes through the viewport. The optical emission spectrometer is positioned on an exterior of the viewport and the optical radiation originates from inside the substrate processing region above the substrate.

The substrate processing chambers may further include a local plasma power supply configured to form a local plasma in the substrate processing region. The local plasma may have a local plasma power less than 10% of the remote plasma power. The substrate processing chambers may further include a fiber optic cable configured to guide the optical radiation from the viewport to the optical emission spectrometer. The substrate processing chambers may further include an electrode proximal to the viewport. The electrode may be positioned on the exterior of the viewport. The substrate processing chambers may further include a plasma power supply configured to apply a plasma power to the electrode. The substrate processing chambers may further include a second electrode configured to apply a plasma power to the electrode. The electrode may be electrically insulated from the second electrode.

Embodiments disclosed herein include optical emission spectrometer assemblies. The optical emission spectrometer assemblies include a flange configured to attach to a substrate processing chamber. The flange is configured to form a vacuum seal with the substrate processing chamber. The optical emission spectrometer assemblies further include a planar viewport attached to the flange forming a vacuum seal with the flange. The planar viewport is optically transmissive in a near infrared spectrum. The optical emission spectrometer assemblies further include an electrode proximal to the planar viewport. The electrode is disposed on an external side of the planar viewport. The optical emission spectrometer assemblies further include an optical emission spectrometer configured to receive optical radiation after the optical radiation passes through the planar viewport. The optical emission spectrometer is positioned on the external side of the planar viewport. The optical emission spectrometer assemblies further include a plasma power supply configured to apply a plasma power to the electrode.

The optical emission spectrometer assemblies may further include a fiber optic cable configured to guide infrared light from the planar viewport to the optical emission spectrometer. The plasma power supply may be configured to apply the plasma power between the electrode and the substrate processing chamber. The optical emission spectrometer assemblies may further include a second electrode proximal to the planar viewport. The electrode may be electrically insulated from the second electrode. The plasma power supply may be configured to apply the plasma power between the electrode and the second electrode.

Additional embodiments and features are set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the specification or may be learned by the practice of the disclosed embodiments. The features and advantages of the disclosed embodiments may be realized and attained by means of the instrumentalities, combinations, and methods described in the specification.

DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the embodiments may be realized by reference to the remaining portions of the specification and the drawings.

FIG. 1 shows a schematic cross-sectional view of a substrate processing chamber according to embodiments.

FIG. 2 is a flow chart of a remote plasma etch process according to embodiments.

FIG. 3A shows a schematic cross-sectional view of a substrate processing chamber according to embodiments.

FIG. 3B shows a schematic cross-sectional view of a substrate processing chamber according to embodiments.

FIG. 4 is an optical emission spectrum according to embodiments.

FIG. 5 is a plot of etch amount correlation with fluorine signal according to embodiments.

FIG. 6A shows a cross-sectional side view of a weak plasma viewport according to embodiments.

FIG. 6B shows a cross-sectional end view of a weak plasma viewport according to embodiments.

FIG. 7A shows a cross-sectional side view of a weak plasma viewport according to embodiments.

FIG. 7B shows a cross-sectional end view of a weak plasma viewport according to embodiments.

FIG. 7C shows a cross-sectional side view of a weak plasma viewport according to embodiments.

FIG. 8A shows a cross-sectional side view of a weak plasma viewport according to embodiments.

FIG. 8B shows a cross-sectional side view of a weak plasma viewport according to embodiments.

In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

DETAILED DESCRIPTION

Methods and systems for etching substrates using a remote plasma are described. Remotely excited etchants are formed in a remote plasma and flowed through a showerhead into a substrate processing region to etch the substrate. Optical emission spectra are acquired from the substrate processing region just above the substrate. The optical emission spectra may be used to determine an endpoint of the etch, determine the etch rate or otherwise characterize the etch process in-situ. A weak plasma may be present in the substrate processing region. The weak plasma may have much lower intensity than the remote plasma. In cases where no bias plasma above the substrate is used in an etch process, a weak plasma may be ignited near a viewport disposed near the side of the substrate processing region to characterize the etchants.

In the past, gas phase etch processes have excited NF₃ in a local plasma inside substrate processing region. Optical emission spectroscopy was performed by flowing some of the reactants in the substrate processing region through tubing to a separate plasma used for the characterization and then disposing any chemical effluents through a vacuum pump. Recently, high selectivity gas-phase etch processes have been developed using a spatially-constrained remote plasma region separated from the substrate processing region by a showerhead (sometimes a dual-channel showerhead). Plasma effluents are formed in the remote plasma region and flow into the substrate processing region through the showerhead. The remote plasma effluents are optionally further excited in a bias plasma above the substrate.

The methods and systems described herein provide the benefit of characterizing remote plasma etch processes in the substrate processing region where there is more space than in the remote plasma region. The characterization of the plasma effluents occurs closer to the substrate, providing a more accurate determination of the etch process compared to the more circuitous sampling routes used previously.

FIG. 1 shows a schematic cross-sectional view of an exemplary substrate processing chamber. The schematic of the substrate processing chamber 1001 serves to introduce the optical emission spectrometer but also provide context for alternative configurations and details provided in subsequent descriptions. Later drawings will provide less detail compared to FIG. 1 but only for the sake of brevity. Any combination of features found in FIG. 1 may be present in any or all subsequent embodiments. The substrate processing chamber 1001 has a remote plasma region 1015 and a substrate processing region 1033 inside. The remote plasma region 1015 is partitioned from the substrate processing region 1033 by an ion suppressor 1023 and a showerhead 1025.

A top plate 1017, ion suppressor 1023, showerhead 1025, and a substrate support 1065 (also known as a pedestal), having a substrate 1055 disposed thereon, are shown and may each be included according to all embodiments described herein. The pedestal 1065 may have a heat exchange channel through which a heat exchange fluid flows to control the temperature of the substrate 1055. This configuration may allow the substrate 1055 temperature to be cooled or heated to maintain relatively low temperatures, such as between −20° C. to 200° C. The pedestal 1065 may also be resistively heated to relatively high temperatures, such as between 100° C. and 1100° C., using an embedded heater element.

The etchant precursors flow from the etchant supply system 1010 through the holes in the top plate 1017 into the remote plasma region 1015. The structural features may include the selection of dimensions and cross-sectional geometries of the apertures in the top plate 1017 to deactivate back-streaming plasma in cases where a plasma is generated in remote plasma region 1015. The top plate 1017, or a conductive top portion of the substrate processing chamber 1001, and the showerhead 1025 are shown with an intervening insulating ring 1020, which allows an AC potential to be applied to the top plate 1017 relative to the showerhead 1025 and/or the ion suppressor 1023. The insulating ring 1020 may be positioned between the top plate 1017 and the showerhead 1025 and/or the ion suppressor 1023 enabling a capacitively-coupled plasma (CCP) to be formed in the remote plasma region 1015. The remote plasma region 1015 houses the remote plasma.

The plurality of holes in the ion suppressor 1023 may be configured to control the passage of the activated gas, i.e., the ionic, radical, and/or neutral species, through the ion suppressor 1023. For example, the aspect ratio of the holes, or the hole diameter to length, and/or the geometry of the holes may be selected so that the flow of ionically-charged species in the activated gas passing through the ion suppressor 1023 is reduced. The holes in the ion suppressor 1023 may include a tapered portion that faces the remote plasma region 1015, and a cylindrical portion that faces the showerhead 1025. The cylindrical portion may be shaped and dimensioned to control the flow of ionic species passing to and through the showerhead 1025. An adjustable electrical bias may also be applied to the ion suppressor 1023 as an additional means to control the flow of ionic species through the suppressor. The ion suppressor 1023 may function to reduce or eliminate the amount of ionically charged species traveling from the plasma generation region to the substrate. Uncharged neutral and radical species may still pass through the openings in the ion suppressor to react with the substrate.

Remote plasma power can be of a variety of frequencies or a combination of multiple frequencies. The remote plasma may be provided by remote RF power delivered from the remote plasma power supply 1068 to the top plate 1017 relative to the ion suppressor 1023, relative to the showerhead 1025, or relative to both the ion suppressor 1023 and the showerhead 1025 (as shown). The remote RF power may be between 10 watts and 10,000 watts, between 10 watts and 5,000 watts, preferably between 25 watts and 2000 watts or more preferably between 50 watts and 1500 watts to increase the longevity of chamber components. The remote RF frequency applied in the exemplary processing system to the remote plasma region may be low RF frequencies less than 200 kHz, higher RF frequencies between 10 MHz and 15 MHz, or microwave frequencies greater than 1 GHz in embodiments. The plasma power may be capacitively-coupled (CCP) or inductively-coupled (ICP) into the remote plasma region.

Plasma effluents derived from the etchant precursors in the remote plasma region 1015 may travel through apertures in the ion suppressor 1023, and/or the showerhead 1025 and into the substrate processing region 1033 through through-holes or the first fluid channels 1019 of the showerhead in embodiments. Little or no plasma may be present in substrate processing region 1033 during the remote plasma etch process. The plasma effluents react with the substrate to etch material from the substrate.

The showerhead 1025 may be a dual channel showerhead (DCSH). The dual channel showerhead 1025 may provide for etching processes that allow for separation of etchants outside of the substrate processing region 1033 to provide limited interaction with chamber components and each other prior to being delivered into the substrate processing region 1033. The showerhead 1025 may comprise an upper plate 1014 and a lower plate 1016. The plates may be coupled with one another to define a volume 1018 between the plates. The plate configuration may provide the first fluid channels 1019 through the upper and lower plates, and the second fluid channels 1021 through the lower plate 1016. The formed channels may be configured to provide fluid access from the volume 1018 through the lower plate 1016 via the second fluid channels 1021 alone, and the first fluid channels 1019 may be fluidly isolated from the volume 1018 between the plates and the second fluid channels 1021. The volume 1018 may be fluidly accessible through a side of the showerhead 1025 and used to supply an unexcited precursor in embodiments.

Optionally, a bias plasma power may be present in the substrate processing region in embodiments. The bias plasma may be used to further excite plasma effluents already excited in the remote plasma. The bias plasma refers to a local plasma located just above the substrate. The term bias plasma is used since the plasma effluents may be ionized and/or accelerated towards the substrate to beneficially accelerate or provide incoming alignment to some etch processes. The bias plasma may be formed by applying bias plasma power from a bias plasma power supply 1069 to the substrate 1055/pedestal 1065 relative to the ion suppressor 1023, relative to the showerhead 1025, or relative to both the ion suppressor 1023 and the showerhead 1025 (as shown). The bias RF plasma power may be lower than the remote RF power. The bias RF plasma power may be below 20%, below 15%, below 10% or below 5% of the remote RF plasma power. The bias RF plasma power may be between 1 watt and 1,000 watts, between 1 watt and 500 watts, or between 2 watts and 100 watts in embodiments. The bias RF plasma frequency applied in the exemplary processing system to the remote plasma region may be low RF plasma frequencies less than 200 kHz, higher RF plasma frequencies between 10 MHz and 15 MHz, or microwave frequencies greater than 1 GHz in embodiments. The bias RF plasma frequency may be different from the remote RF frequency to further improve the integrity of the optical emission spectra. The plasma power may be capacitively-coupled (CCP) or inductively-coupled (ICP) into the substrate plasma region.

A viewport 1071 is disposed on the side of the substrate processing chamber 1001 and forms a border of the substrate processing region 1033. The viewport 1071 transmits optical radiation and may be transmissive in the infrared portion of the optical spectrum. Viewports described herein may be transmissive between 650 nm and 800 nm, between 680 nm and 760 nm or between 700 nm and 740 nm in embodiments. An optical emission spectrometer (OES) is disposed outside the viewport 1071 and configured to receive optical radiation, preferably infrared radiation, originating from the bias plasma formed in the substrate processing region 1033. In cases where there is no bias plasma, a weak plasma may be formed on the interior side of the viewport 1071 to facilitate the acquisition of the optical emission spectrum by the optical emission spectrometer. The characteristics of the weak plasma (power, frequency) may be the same as the bias power properties provided earlier, according to embodiments. For example, the weak RF plasma power may be below 20%, below 15%, below 10% or below 5% of the remote RF plasma power. The weak RF plasma power may be between 1 watt and 1,000 watts, between 1 watt and 500 watts, or between 2 watts and 100 watts in embodiments. The weak RF plasma frequency applied in the exemplary processing system to the remote plasma region may be low RF plasma frequencies less than 200 kHz, higher RF plasma frequencies between 10 MHz and 15 MHz, or microwave frequencies greater than 1 GHz in embodiments. The weak RF plasma frequency may be different from the remote RF frequency to further improve the integrity of the optical emission spectra. The weak plasma power may be capacitively-coupled (CCP) or inductively-coupled (ICP) into the substrate plasma region.

To better understand and appreciate the embodiments disclosed herein, reference is now made to FIG. 2 which is a flow chart of a highly selective etch process 2010 according to embodiments. Prior to the first operation, the substrate is patterned and then placed within the substrate processing region in optional operation 2100. A fluorine-containing precursor (e.g. NF₃) may be flowed into the remote plasma region in operation 2200. A remote plasma is formed from the fluorine-containing precursor in the remote plasma region by applying a remote plasma power across the remote plasma region to form plasma effluents. The plasma effluents are flowed through a showerhead disposed between the remote plasma region and the substrate processing region in operation 2300. The plasma effluents flow through the showerhead from the remote plasma region into the substrate processing region. A bias plasma is formed by applying a bias plasma power across the substrate processing region to further excite the plasma effluents in operation 2400. The bias plasma power is less than the remote plasma power and the bias plasma may be referred to as a “weak” plasma in embodiments. Portions of a patterned substrate are selectively etched in operation 2500. An optical emission spectrum is acquired through a viewport in the side of the substrate processing chamber (operation 2600) and the etch is stopped based on the results. The viewport forms a border of the substrate processing region. Optionally, the patterned substrate is removed from the substrate processing region (operation 2700).

FIG. 3A shows a schematic cross-sectional view of an exemplary substrate processing chamber. Process and equipment parameters given earlier apply to all embodiments described herein. Similarly, process and equipment parameters given here and in subsequent discussions may be used for all other embodiments described herein. The substrate processing chamber 3001 has a remote plasma region 3015 and a substrate processing region 3033 inside. The remote plasma region 3015 is partitioned from the substrate processing region 3033 by a showerhead 3025 with through-holes 3019 configured to pass plasma effluents.

A top plate 3017, showerhead 3025, and a pedestal 3065 supporting a substrate 3055 are shown. A fluorine-containing precursor may flow from the etchant supply system 3010 into the remote plasma region 3015. The top plate 3017 and the showerhead 3025 are electrically-separated conductors separated by insulating ring 3020. An AC potential (the remote plasma power) is applied to the top plate 3017 relative to the showerhead 3025 to form the remote plasma. The remote plasma may be a capacitively-coupled plasma (CCP) in the remote plasma region 3015. Plasma frequencies and plasma powers provided by a remote plasma power supply (not shown) were provided previously.

Plasma effluents derived from the fluorine precursors in the remote plasma region 3015 may travel through the through-holes 3019 in the showerhead 3025 and into the substrate processing region 3033. A bias plasma power is applied by a bias plasma power supply (not shown) to the substrate processing region 3033. The bias plasma further excites the plasma effluents. The bias plasma weakly ionizes and accelerates plasma effluents towards the substrate to beneficially accelerate or provide incoming alignment to the etch processes. The bias plasma may be formed by applying bias plasma power from a bias plasma power supply to the substrate 3055/pedestal 3065 relative to the showerhead 3025. The plasma effluents react with the substrate to etch material from the substrate.

Acquisition of optical emission spectra uses the recombination of electrons with ions to emit photons indicative of a presence of specific atomic species. In the embodiment represented in FIG. 3A, the bias plasma is sufficient to supply the ionization needed to acquire an optical emission spectrum. To further enable the measurement, a viewport 3071 is disposed in the side of the substrate processing chamber 3001. The optical emission spectrum is measured using an optical emission spectrometer on the outside of the viewport 3071.

FIG. 3B shows a schematic cross-sectional view of an exemplary substrate processing chamber. The substrate processing chamber 3001 has a remote plasma region 3015 and a substrate processing region 3033 inside. The remote plasma region 3015 is partitioned from the substrate processing region 3033 by a showerhead 3025 with through-holes 3019 to pass plasma effluents. A top plate 3017, showerhead 3025, and a pedestal 3065 supporting a substrate 3055 are shown. A fluorine-containing precursor may flow from the etchant supply system 3010 into the remote plasma region 3015. An AC potential (the remote plasma power) is applied to the top plate 3017 relative to the showerhead 3025 to form the remote plasma.

Plasma effluents derived from the fluorine precursors in the remote plasma region 3015 travel through the through-holes 3019 in the showerhead 3025 and into the substrate processing region 3033. The plasma effluents react with the substrate to etch material from the substrate.

No bias plasma power is applied to the substrate processing region 3033 in embodiments. The substrate processing region 3033 may be referred to as plasma-free and may be devoid of plasma in embodiments. A weak plasma near the substrate processing region is used to obtain an optical emission spectrum. The weak plasma results in recombination of electrons with ions and concomitant emission of photons indicative of a presence of specific atomic species. Therefore a weak plasma is formed just on the inside of a viewport 3071 by a variety of techniques to be described herein. The viewport 3071 is disposed in the side of the substrate processing chamber 3001. The optical emission spectrum is measured using an optical emission spectrometer on the outside of the viewport 3071. The weak plasma is formed by applying weak plasma power from a weak plasma power supply to one or more electrode(s) (not shown) near the viewport 3071. The weak RF plasma power may be lower than the remote RF power. A relatively low weak RF plasma power avoids swamping the remote plasma OES signal with characteristics of the weak local plasma. The weak RF plasma power may be below 10%, below 8%, below 5% or below 3% of the remote RF plasma power. The weak RF plasma power may be between 0.1 watts and 300 watts, between 0.2 watts and 100 watts, or between 0.5 watts and 20 watts in embodiments. The weak RF plasma frequency applied in the exemplary processing system to the remote plasma region may be low RF plasma frequencies less than 200 kHz, higher RF plasma frequencies between 10 MHz and 15 MHz, or microwave frequencies greater than 1 GHz in embodiments. The weak RF plasma frequency may be different from the remote RF frequency to further improve the integrity of the optical emission spectra. For example, the weak RF plasma frequency may be 60 kHz and the remote RF frequency may be 13 MHz. The plasma power may be capacitively-coupled (CCP) or inductively-coupled (ICP) into the substrate plasma region.

The pressure in the substrate processing region and the remote plasma region during the etching operations may be between 0.01 Torr and 50 Torr, between 0.1 Torr and 15 Torr or between 0.5 Torr and 10 Torr in embodiments. The temperature of the patterned substrate during the etching operations may be between −20° C. and 450° C., between 0° C. and 350° C. or between 5° C. and 200° C. in embodiments.

Reference is now made to FIG. 4 which is plot of an optical emission spectra. An optical emission spectrum 4010 is depicted which represents a concurrent remote plasma and a weak local plasma. Another optical emission spectrum 4020 is depicted which represents only a weak local plasma. The peaks near 703.7 nm, 712.8 nm, and 720.2 nm correspond with fluorine atom concentration. The peaks near 706.5 nm and 728.1 nm correspond with helium atom concentration. Helium or another inert gas may be used to benefit the etch process but may also be useful to compare and normalize the fluorine peaks. Qualitatively, the fluorine measurements can be seen to become more pronounced when the remote plasma is in use. More generally, the fluorine measurements may be used to determine whether the fluorine concentration is changing, has reached a plateau, or has reached a predetermined setpoint during an etch process.

FIG. 5 is a plot of etch amount correlation with fluorine signal according to embodiments. The fluorine signal normalized to helium signal is shown on the x-axis whereas the etch amount corresponds to the y-axis. A plot of etch amount (proportion to etch rate) versus normalized fluorine signal 5010 is shown to be roughly linear with an offset. The linearity enables the normalized fluorine signal to be an in-situ indicator of the etch rate of a substrate without measuring the substrate directly.

FIGS. 6A and 6B show cross-sectional side views of a weak plasma viewport according to embodiments. FIG. 6A shows a substrate processing region 6033 with a tubular viewport 6071 affixed to the side and forming a vacuum seal with the wall of the substrate processing chamber. A first electrode 6072-1 and a second electrode 6072-2 are affixed to the tubular viewport 6071 on opposite sides. All electrodes described herein may be copper adhesive tape or silver paste to facilitate attaching the electrodes to the various viewports according to embodiments. Other adhesive formats may also be used. Alternatively, the electrodes may simply be placed near the tubular viewport 6071 on opposite sides since mechanical contact between the viewport and the electrodes is not necessary to form the plasma. A weak plasma 6034 is formed on the inside of the tubular viewport 6071 by applying a weak RF plasma power from a weak RF plasma power supply (not shown) between the first electrode 6072-1 and the second electrode 6072-2. FIG. 6B shows an end view of the same configuration and includes a view of the weak plasma power supply 6068. A fiber optic cable 6073 is configured to guide optical radiation from the weak plasma 6034 through the tubular viewport 6071 and into the optical emission spectrometer 6070.

FIGS. 7A, 7B, and 7C show cross-sectional side views of a weak plasma viewport according to embodiments. FIG. 7A shows a substrate processing region 7033 with a tubular viewport 7071 affixed to the side and forming a vacuum seal with the wall of the substrate processing chamber. An electrode 7072-1 is affixed to the tubular viewport 7071 around the exterior of the tubular viewport 7071. The electrode 7072-1 may be a piece of conducting adhesive tape (e.g. copper) or a layer of conductive paste (e.g. silver) to facilitate attaching the electrode 7072-1 to the tubular viewport 7071 according to embodiments. The electrode 7072-1 may simply be a conducting hoop looped loosely around the tubular viewport 7071 since forming the weak plasma does not rely on mechanical contact between the tubular viewport 7071 and the electrode 7072-1. A weak plasma 7034-1 is formed on the inside of the tubular viewport 7071 by applying a weak RF plasma power from a weak RF plasma power supply 7068-1 between the electrode 7072-1 and the rest of the substrate processing chamber or the wall shown as a border of the substrate processing region 7033. Also shown is a fiber optic cable 7073 configured to guide optical radiation from the weak plasma 7034 through the tubular viewport 7071 and into the optical emission spectrometer 7070. FIG. 7B shows an end view of the same configuration and includes a view of the electrode 7072-1 which is shaped like a hoop. FIG. 7C shows a related configuration having an electrode 7072-2 over the end of the tubular viewport 7071 and the fiber optic cable 7073 is relocated to peer at the weak plasma 7034-2 from a different angle through an unobstructed portion of the tubular viewport 7071. A weak RF plasma power supply 7068-2 provides the weak RF plasma power between the electrode 7072-2 and the wall of the substrate processing chamber.

FIGS. 8A and 8B show cross-sectional side views of a weak plasma viewport according to embodiments. FIG. 8A shows a substrate processing region 8033 with a planar viewport 8071 affixed to the side and forming a vacuum seal with the wall of the substrate processing chamber. A first electrode 8072-1 and a second electrode 8072-2 are affixed to the planar viewport 8071 without any direct electrical connection between them. The first electrode 8072-1 and the second electrode may be pieces of conducting adhesive tape (e.g. copper), a layer of conductive paste (e.g. silver) or electrodes placed near or adjacent to the planar viewport 8071. The electrodes (8072-1, 8072-2) do not need to be in mechanical contact with the planar viewport 8071, in embodiments, to provide the capability of forming a weak plasma 8034-1. The weak plasma 8034-1 is formed on the inside of the planar viewport 8071 by applying a weak RF plasma power from a weak RF plasma power supply 8068-1 between the first electrode 8072-1 and the second electrode 8072-2. Also shown is a fiber optic cable 8073 configured to guide optical radiation from the weak plasma 8034-1 through the planar viewport 8071 and into the optical emission spectrometer 8070. FIG. 8B shows a substrate processing region 8033 with a planar viewport 8071 affixed to the side and forming a vacuum seal with the wall of the substrate processing chamber. An electrode 8072-3 is affixed to the planar viewport 8071. The first electrode 8072-1 may again be a piece of conducting adhesive tape, a layer of conductive paste, or an electrode placed very near or contacting the planar viewport 8071. The weak plasma 8034-1 is formed on the inside of the planar viewport 8071 by applying a weak RF plasma power from a weak RF plasma power supply 8068-2 between the electrode 8072-3 and the rest of the substrate processing chamber or the wall shown as a border of the substrate processing region 8033. Also shown is a fiber optic cable 8073 configured to guide optical radiation from the weak plasma 8034-2 through the planar viewport 8071 and into the optical emission spectrometer 8070.

The tubular viewports described herein may be more prone to breakage since they stick out from the substrate processing chamber. The planar viewports provide the benefit of reducing the chance of accidentally breaking the viewport. The thickness of the planar viewports described herein affect the intensity of the weak plasmas inside the substrate processing chamber near the substrate. The thickness of the planar viewports may be between 1 mm and 15 mm, between 2 mm and 10 mm or preferably between 3 mm and 8 mm according to embodiments. The height and/or width of the planar viewports (as viewed from the axis of the thinnest dimension) may be between 20 mm and 100 mm or between 30 mm and 70 mm in embodiments. The fiber optic cable in all embodiments described herein may be positioned to the side of the substrate and just above the major plane of the substrate to preferentially sample the portion of the plasma effluents most likely to be participating in the etch process. The fiber optic cable may point horizontally (parallel to the major plane of the substrate) between 1 mm and 10 mm above the top surface of the substrate according to embodiments.

In embodiments, an ion suppressor (which may be the showerhead) may be used to provide radical and/or neutral species for gas-phase etching. The ion suppressor may also be referred to as an ion suppression element and may be positioned between the remote chamber region and the substrate processing region along with the showerhead. In embodiments, for example, the ion suppressor is used to filter etching plasma effluents en route from the remote plasma region(s) to the substrate processing region. The ion suppressor may be used to provide a reactive gas having a higher concentration of radicals than ions. Plasma effluents pass through the ion suppressor disposed between the remote plasma region and the substrate processing region. The ion suppressor functions to dramatically reduce or substantially eliminate ionic species traveling from the plasma generation region to the substrate. The ion suppressors described herein are simply one way to achieve a low electron temperature in the substrate processing region during the gas-phase etch processes described herein.

In embodiments, an electron beam is passed through the substrate processing region in a plane parallel to the substrate to reduce the electron temperature of the plasma effluents. A simpler showerhead may be used if an electron beam is applied in this manner. The electron beam may be passed as a laminar sheet disposed above the substrate in embodiments. The electron beam provides a source of neutralizing negative charge and provides a more active means for reducing the flow of positively charged ions towards the substrate and increasing the etch selectivity in embodiments. The flow of plasma effluents and various parameters governing the operation of the electron beam may be adjusted to lower the electron temperature measured in the substrate processing region.

The electron temperature may be measured using a Langmuir probe in the substrate processing region during excitation of a plasma in the remote plasma. In all plasma-free regions described herein (especially in the substrate processing region), the electron temperature may be less than 0.5 eV, less than 0.45 eV, less than 0.4 eV, or less than 0.35 eV. These extremely low values for the electron temperature are enabled by the presence of the electron beam, showerhead and/or the ion suppressor. Uncharged neutral and radical species may pass through the electron beam and/or the openings in the ion suppressor to react at the substrate. Such a process using radicals and other neutral species can reduce plasma damage compared to conventional plasma etch processes that include sputtering and bombardment. Embodiments disclosed herein are also advantageous over conventional wet etch processes where surface tension of liquids can cause bending and peeling of small features.

The substrate processing region may be described herein as “plasma-free” during the etch processes described herein. “Plasma-free” does not necessarily mean the region is devoid of plasma. A weak plasma may be present to perform the optical emission spectroscopy measurement but the region directly above the substrate may be devoid of plasma since the weak plasma is positioned off to the side of the substrate processing region in embodiments. Ionized species and free electrons created within the plasma region may travel through pores (apertures) in the partition (showerhead) at exceedingly small concentrations. The borders of the plasma in the remote plasma region (e.g. the remote chamber region and/or the remote plasma region) may encroach to some small degree upon the substrate processing region through the apertures in the showerhead. Furthermore, a low intensity plasma may be created in the substrate processing region without eliminating desirable features of the etch processes described herein. All causes for a plasma having much lower intensity ion density than the remote plasma region during the creation of the excited plasma effluents do not deviate from the scope of “plasma-free” as used herein.

As used herein “substrate” may be a support substrate with or without layers formed thereon. The patterned substrate may be an insulator or a semiconductor of a variety of doping concentrations and profiles and may, for example, be a semiconductor substrate of the type used in the manufacture of integrated circuits. Exposed “silicon oxide” of the patterned substrate is predominantly SiO₂ but may include concentrations of other elemental constituents such as, e.g., nitrogen, hydrogen and carbon. In some embodiments, silicon oxide portions etched using the methods disclosed herein consist essentially of silicon and oxygen. Exposed “silicon nitride” of the patterned substrate is predominantly Si₃N₄ but may include concentrations of other elemental constituents such as, e.g., oxygen, hydrogen and carbon. In some embodiments, silicon nitride portions described herein consist essentially of silicon and nitrogen. Generally speaking, a first exposed portion of a patterned substrate is etched faster than a second exposed portion. The first exposed portion may have an atomic stoichiometry which differs from the second exposed portion. In embodiments, the first exposed portion may contain an element which is not present in the second exposed portion. Similarly, the second exposed portion may contain an element which is not present in the first exposed portion according to embodiments.

The term “precursor” is used to refer to any chemical which takes part in a reaction to either remove material from or deposit material onto a surface. “Plasma effluents” describe gas exiting from the remote plasma region and entering the remote chamber region and/or the substrate processing region. Plasma effluents are in an “excited state” wherein at least some of the gas molecules are in vibrationally-excited, dissociated and/or ionized states. A “radical precursor” is used to describe plasma effluents (a gas in an excited state which is exiting a plasma) which participate in a reaction to either remove material from or deposit material on a surface. “Radical-fluorine precursors” describe radical precursors which contain fluorine but may contain other elemental constituents. The phrase “inert gas” refers to any gas which does not form chemical bonds when etching or being incorporated into a film. Exemplary inert gases include noble gases but may include other gases so long as no chemical bonds are formed when (typically) trace amounts are trapped in a film.

Having disclosed several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the disclosed embodiments. Additionally, a number of well-known processes and elements have not been described to avoid unnecessarily obscuring the present embodiments. Accordingly, the above description should not be taken as limiting the scope of the claims.

Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the claims, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.

As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a process” includes a plurality of such processes and reference to “the dielectric material” includes reference to one or more dielectric materials and equivalents thereof known to those skilled in the art, and so forth.

Also, the words “comprise,” “comprising,” “include,” “including,” and “includes” when used in this specification and in the following claims are intended to specify the presence of stated features, integers, components, or steps, but they do not preclude the presence or addition of one or more other features, integers, components, steps, acts, or groups. 

The invention claimed is:
 1. A method of etching a substrate, the method comprising: placing the substrate in a substrate processing region of a substrate processing chamber; flowing a fluorine-containing precursor into a remote plasma region separated from the substrate processing region by a showerhead; forming a remote plasma having a remote plasma power in the remote plasma region; producing plasma effluents from the fluorine-containing precursor in the remote plasma in the remote plasma region; flowing the plasma effluents through the showerhead into the substrate processing region; etching the substrate with the plasma effluents; forming a local plasma having a local plasma power in the substrate processing region while maintaining the remote plasma and etching the substrate, wherein the remote plasma power of the remote plasma exceeds the local plasma power of the local plasma by a factor of ten or more; acquiring an optical emission spectrum through a viewport affixed to a side of the substrate processing chamber and forming a border of the substrate processing region, wherein the optical emission spectrum represents intensity as a function of optical wavelength, and wherein the optical emission spectrum is acquired with an optical emission spectrometer; determining a fluorine signal from the optical emission spectrum; and determining an etch rate of the substrate based on the fluorine signal, wherein the fluorine signal is linearly correlated with the etch rate of the substrate.
 2. The method of claim 1, wherein the local plasma is centered over the substrate.
 3. The method of claim 1, wherein the local plasma is disposed above the substrate and outside an edge of the substrate near the viewport.
 4. The method of claim 3, wherein the local plasma is formed using an electrode that is different from electrodes used for forming the remote plasma and that is disposed on the outside of the viewport, and wherein the local plasma power is applied between the electrode and the substrate processing chamber.
 5. The method of claim 3, wherein the local plasma is formed using a first electrode and a second electrode that are different from electrodes used for forming the remote plasma, wherein the first electrode and the second electrode are each disposed on the outside of the viewport, and wherein the local plasma power is applied between the first electrode and the second electrode.
 6. The method of claim 1, wherein the local plasma is formed outside a radial edge of the substrate and proximate the viewport, and wherein a region that is within the substrate processing region and above the substrate is plasma free.
 7. The method of claim 1, further comprising etching the substrate with the local plasma, wherein the local plasma is a bias plasma.
 8. A method of etching a substrate, the method comprising: placing the substrate in a substrate processing region of a substrate processing chamber; flowing a fluorine-containing precursor into a remote plasma region separated from the substrate processing region by a showerhead; forming a remote plasma having a remote plasma power in the remote plasma region; producing plasma effluents from the fluorine-containing precursor in the remote plasma in the remote plasma region; flowing the plasma effluents through the showerhead into the substrate processing region; etching the substrate with the plasma effluents, wherein an electron temperature within the substrate processing region is less than 0.5 eV while etching the substrate; forming a local plasma having a local plasma power in the substrate processing region while maintaining the remote plasma and etching the substrate, wherein the remote plasma power of the remote plasma exceeds the local plasma power of the local plasma by a factor of ten or more; acquiring an optical emission spectrum through a viewport affixed to a side of the substrate processing chamber and forming a border of the substrate processing region, wherein the optical emission spectrum represents intensity as a function of optical wavelength and the optical emission spectrum is acquired with an optical emission spectrometer; determining at least one signal from the optical emission spectrum; and determining an etch rate of the substrate based on the at least one signal, wherein the at least one signal is linearly correlated with the etch rate of the substrate.
 9. The method of claim 8, wherein a pressure in the substrate processing region and in the remote plasma region while etching the substrate is between 0.01 Torr and 50 Torr.
 10. The method of claim 8, wherein a temperature of the substrate while etching the substrate is between −20° C. and 450° C.
 11. The method of claim 8, wherein the at least one signal comprises a fluorine signal from the optical emission spectrum.
 12. The method of claim 8, wherein the at least one signal comprises a fluorine signal representing a concentration of excited fluorine from both the remote plasma and the local plasma.
 13. The method of claim 8, further comprising passing an electron beam above the substrate.
 14. The method of claim 8, further comprising passing an electron beam as a laminar sheet above the substrate.
 15. A method of etching a substrate, the method comprising: flowing a fluorine-containing precursor into a remote plasma region of a substrate processing chamber; forming a remote plasma having a remote plasma power in the remote plasma region to produce plasma effluents; flowing the plasma effluents into a substrate processing region separated from the remote plasma region by a showerhead, wherein the substrate is housed in the substrate processing region; etching the substrate with the plasma effluents; forming a local plasma having a local plasma power in the substrate processing region while maintaining the remote plasma and etching the substrate, wherein the local plasma is formed outside a radial edge of the substrate and proximate a viewport affixed to a side of the substrate processing chamber and forming a border of the substrate processing region, wherein a region that is within the substrate processing region and above the substrate is plasma free; acquiring an optical emission spectrum through the viewport; determining at least one signal from the optical emission spectrum; and determining an etch rate of the substrate based on the at least one signal, wherein the at least one signal is linearly correlated with the etch rate of the substrate.
 16. The method of claim 15, wherein the remote plasma power of the remote plasma exceeds the local plasma power of the local plasma by a factor of ten or more.
 17. The method of claim 15, wherein the at least one signal comprises a fluorine signal.
 18. The method of claim 15, further comprising passing an electron beam as a laminar sheet above the substrate in the substrate processing region, and wherein an electron temperature within the substrate processing region is less than 0.5 eV while etching the substrate. 